This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Eighteen Rhesus macaques are assigned to one of three groups on this protocol. Animals were immunized with either empty vectors (controls), VSV/SFV E660 or VSV/SFV E660 + GMCSF in April, June and August 2009. All animals were challenged with SIVsmE660 in September 2009. All six animals receiving control vaccines became infected, with peak plasma viral loads ranging between 6.0 and 8.2 log copies/ml. PVL of three control animals has steadily declined after challenge (two of which are currently below detectable limits) and PVL of two control animals remains high between 6.0 and 7.0 log copies/ml. Finally one control animal was humanely euthanized due to neurologic dysfunction. The etiology of the dysfunction is not yet known (histology is pending). Five of the six animals receiving VSV/SFV E660 + GMCSF became infected with peak PVL ranging between 4.7 and 7.8 log copies/ml. One of these animals currently has PVL below detectable limits and the PVL of another animal in this group has steadily declined after challenge. Three animals exhibit PVL remaining steady between 4.0 and 6.0 log copies/ml. Two of six animals receiving VSV/SFV E660 became infected with peak PVL of 3.9 and 5.8 log copies/ml. The PVL of both of these animals returned to undetectable levels by day 35 and 42 post-challenge. All animals will continue to be monitored to follow the progression of infection or lack thereof.